1. Field of the Invention
The present invention relates, in general, to a polypropylene fiber and, more particularly, to a polypropylene fiber which is useful as a material for non-woven fabrics, thereby allowing the non-woven fabrics to be smooth and excellent in strength and providing workability and physical properties for the non-woven fabrics during after-processes. Also, the present invention is concerned with a method for preparing such fibers.
2. Description of the Prior Art
In order that staple fibers are prepared from polyolefin polymers, they have to undergo a series of processes: the polyolefin polymers are generally compounded with some amount of additives and the resulting mixtures are melt-extruded in ordinary commercial processes to give fibers, which are crimped and cut into predetermined lengths.
When being applied for the making of non-woven fabrics, polyolefin staples are typically processed in a carding machine to give non-woven webs which are then thermally bonded.
For thermal bonding, a pair of calender rollers, ultrasonification, or hot air is usually used.
Particularly as for polypropylene filaments or staples, they are arranged after opening and carding processes, and bridged to afford webs. These webs are thermally bonded with the aid of a calender roller with diamond or delta type patterns to produce non-woven fabrics which are industrially useful in various fields. Alternatively, hot air may be utilized instead of calender rollers. In this case, after being allowed to undergo a carding process, webs are bonded to give non-woven fabrics by means of hot air which is circulated in a porous drum.
Polypropylene non-woven fabrics find numerous applications in the disposable diaper, diaper for patients suffering from urinary incontinence, hygienic band, mask, and medical fabric industries. Although not demanding strength as high as that of woven fabrics, the non-woven fabrics used in these purposes have to be soft and satisfy the requirement of safety to skin because they are in direct contact with the skin.
The strength of non-woven fabrics varies depending on their preparation processes as well as on physical properties of material fibers.
With the aim of improving productivity, non-woven fabric producing manufacturers generally try to make high production speed. The high production speed, however, demands more excellent physical properties for the fibers for non-woven fabrics.